As is known, the drive shaft in internal combustion engines is subject to torsional vibrations due to the periodic stress caused by the combustion in the cylinders. These vibrations are particularly intense at start-up and at low speeds, and in the presence of particular construction solutions such as dual-clutch transmissions or start-stop systems.
The torsional vibrations translate into irregular rotations of the ancillaries transmission drive pulley which are transmitted to the ancillaries by means of the drive belt, which is therefore subject to periodic tension variations.
In order to “filter” the torsional oscillations transmitted from the crank shaft to the belt, a filtering pulley is generally used as drive pulley, provided with a hub integral with the drive shaft, a pulley ring cooperating with the belt and one or more elastic elements via which the drive torque is transmitted from the hub to the pulley ring.
To effectively filter the oscillations, the rigidity of the elastic elements should be low; however, the high loads absorbed by the ancillaries do not allow the rigidity to be lowered beyond a certain limit. The need is therefore felt in the sector to develop improved filtering pulleys which meet the conflicting needs described above.